1. Field of the Invention
The present invention relates to a data processing system having a plurality of storage systems, and more particularly to data copying between a plurality of storage systems.
2. Description of the Related Art
In recent years, a technology relating to data copying between storage systems has gained importance by allowing a data processing system to be able to provide services to a customer even when a failure has occurred in the first storage system, in order to provide continual service to the customer. Technology for copying the information stored in the first storage system into the second and third storage systems was disclosed in the following patent references.
U.S. Pat. No. 5,170,480 discloses a technology in which a first computer connected to a first storage system transfers the data stored in the first storage system to a second computer via a communication link between the first computer and the second computer, and the second computer transfers the data to the second storage system connected to the second computer.
U.S. Pat. No. 6,209,002 discloses a technology in which a first storage system transfers the data stored in the first storage system to the second storage system, and the second storage system transfers the data to the third storage system. The computer and the first storage system are connected by a communication link, the first storage system and the second storage system are connected by a communication link, and the second storage system and the third storage system are connected by a communication link. The first storage system holds a first logical volume which is the copying object. The second storage system holds a second logical volume which is the copy of the first logical volume and a third logical volume which is the copy of the second logical volume. The third storage system holds a fourth logical volume which is the copy of the third logical volume. In this patent reference, the second storage system executes exclusively the data copying processing from the second logical volume to the third logical volume and the data copying processing from the third logical volume to the fourth logical volume.
The technology disclosed in U.S. Pat. No. 5,170,480 constantly uses the first computer and the second computer for data copying. The first computer conducts usual operations and the load of data copying processing applied to the first computer cannot be ignored. Another problem is that because data for copying use a communication link between the first computer and the first storage system, those data collide with the data transfer necessary for usual operations and the data reference and data update time necessary for usual operations are extended.
With the technology disclosed in U.S. Pat. No. 6,209,002, the storage capacity multiple of the data quantity which is to be copied is required for the second storage system and the third storage system. Furthermore, when the data quantity which is the object of copying is large, the time consumed by the data copying processing is increased and data in the third storage system become old. The resulting problem is that when operations are restarted by using the data of the third storage system, a long time is required to renew the data of the third storage system and the time required to restart the operations is extended. Furthermore, according to the description provided in this reference, the first storage system in addition to data update processing in the first storage system also conducts data update completion reporting to the host computer when data update processing with the second storage system has ended. Therefore, a long time is consumed for data update from the computers, and the time required for data update extends with the increase in the distance between the first storage system and the second storage system. The resulting problem is that the distance between the two storage systems cannot be made too large.